This invention relates to a process and apparatus for preparing samples to be analyzed for ionic species such as by liquid column chromatography.
At the present time, it is known that several typical liquid samples containing ionic species cause serious problems when analyzed by ion chromatography apparatus. Included in these samples are those having a pH value greater than pH 10 or lower than pH 4, samples with high carbonate concentration and samples containing high concentrations of divalent cations such as calcium and/or magnesium. Presently these samples are prepared for subsequent analysis by adding thereto acidic or basic solutions in order to permit identification of the ionic species for which the analysis is being made without interference by other ionic species in solution. These sample preparation processes are undesirable since they introduce significant interference from the counter ions from the added acid (anions) or base (cations). This can cause considerable interference which can limit the capability of the analysis apparatus to properly determine the individual constituents and their amounts in the sample.
Attempts to utilize ion exchange resin beads to remove undesired ions is an improvement in that it eliminates the addition of excessive counter ions as these counter ions are covalently bound to the bead. In this process, the sample volume selected for analysis is passed through, on or over the polymeric like structure which includes counter ions bonded to either a silicate or an organic polymer bead. The potentially interfering counter ions are sufficiently bonded to the beads as to preclude direct analytical interference. However, the beads are themselves a source of organic and inorganic contamination. Even a repeated and very extensive precleaning of the ion exchange resin beads does not prevent sample contamination at the levels detachable by presently available ion chromatography apparatus. In addition, the resin beads have adsorption-desorption capacity so that a portion of the ions being analyzed are adsorbed into the pores of the resin beads. The net effect is the possibility of skewing and/or loss of the resultant data during the analytical process thereby negating any anticipated advantage by selecting these materials as a means for improving the chromatographic analytical process.
It has also been known prior to this invention to utilize hollow fibers having an ion exchange capacity to purify a continuous stream of a gas passing therethrough.
A hollow fiber is defined as a seamless thin walled member of essentially tubular geometry with an inlet and outlet means where the constituent to be purified or reacted upon is communicated into the center of the tubular membrane system through the inlet, subsequently acted upon in a chemical manner by the tubular portion itself and/or by other reacting mechanism(s) present during the time the constituent is residing in the tubular portion of the fiber and subsequently removed through or passed from the tubular geometry by or through the outlet means. Such hollow fiber systems may be of singular or multiple path geometries and may also be immersed in solutions and/or gasses or connected with systems designed to promote the exchange process. An example is the use of sulfuric acid surrounding a hollow fiber to promote the exchange of protons across the hollow fiber tubular member portion. Such an added solution to a hollow fiber system component in this way is defined as a counter ion donating solution or CIDS. However, it is also known that the solution comprising the source of regenerated ions can penetrate the hollow fibers such that the proton donator, e.g., sulfuric acid, contaminates the liquid by passing sulfate ions through the hollow fiber.
Accordingly, it would be desirable to provide a method for effecting sample preparation for ion analysis without the need for adding an acidic or basic solution to the sample since such prior art methods introduce significant interferences into the sample. In addition, it would be desirable to provide such a method wherein impurities from the ion exchange medium into the sample are eliminated. Furthermore, it would be desirable to provide such a sample preparation means which can be used with a wide variety of liquid samples. In addition, it would be desirable to provide a sample preparation means which can rapidly process a large number of samples before being replaced. Also, it would be desirable to provide a sample preparation means which provides a simple means by which the operator can replace depleted ion exchange polymer.